The real-time confocal microscope using the dispersion optics of the present invention can be applied to inspections requiring a high speed such as an inspection of defects in a semiconductor wafer, and an inspection of defects in an LCD, and the like.
Conventionally, the confocal scanning microscope has been widely used in observing objects in the field of biomedical science. Further, it has advantages that it is possible to observe an inside shape of a specimen as the depth discrimination in the direction of the optical axis is good, and to obtain a three dimensional shape of the object. Also, the confocal scanning microscope has been widely applied to the measurement and inspection of the semiconductor wafer, a flat panel display device, and micro patterns, and the like, because it has a high resolution in the horizontal direction in comparison with the conventional optical microscope.
FIG. 1 is a schematic view of the confocal scanning microscope using a conventional Nipkow disk. As shown in the drawing, the conventional microscope is composed of a light source 1, a collimation lens 2, a beam splitter 3, a Nipkow disk 4, a motor 5, a tube lens 6, an objective lens 7, a specimen 8, a first lens 9, a second lens 10, and a two dimensional photoelectric detector 11.
In this conventional confocal microscope, the light emitted from the light source 1 passes through the collimation lens 2 to become parallel lights. The parallel lights are reflected at the beam splitter 3 to illuminate an upper surface of the Nipkow disk 4.
In this instance, a shape of the Nipkow disk 4 is shown in FIG. 2. FIG. 2 shows a shape of the disk on which a plurality of pinhole shaped small apertures 4a are distributed. When the parallel beams illuminate the disk, only lights passing through the plurality of apertures within an illuminating region can propagate toward the tube lens 6. The lights passing through the respective aperture in the illuminating region can diverge with various angles due to a diffraction phenomenon to produce effects identical with those of arranging a point light source at the position of the aperture.
The tube lens 6 and the objective lens 7 form the image of the aperture on the specimen 8 to produce effect as was produced when the plurality of point regions are only illuminated among the observation regions of the specimen. In order to illuminate whole observation regions of the specimen, it is necessary to change the position of the aperture. In this regard, the apertures 4a on the disk are made to move by the movement of the rotation shaft of the motor 5 after mounting the Nipkow disk 4 to the motor 5.
Accordingly, the light reflected from an illuminating portion on the specimen 8 passes through the objective lens 7 and the tube lens 6 to thereby form an image on the Nipkow disk 4. In this instance, if the specimen 8 is positioned on the focal plane of the objective lens 7, the reflected light passes through the aperture on the Nipkow disk 4, however, if the specimen 8 gets out of the focal plane to move to the direction of optical axis, the reflected light cannot pass through the aperture. As a result, the confocal effect can be obtained, and it is possible to obtain a high resolution in the direction of the optical axis.
Further, the light passed through the aperture forms an image on the two dimensional photoelectric detector 11 by means of the first lens 9 and the second lens 10. The position of the point formed on the photoelectric detector 11 is changed according to the driving rotation of the motor 5 so that the light signal can be transferred to whole region of the two dimensional photoelectric detector to make it possible to obtain a two dimensional information of the specimen.
FIG. 3 shows a different shape of the Nipkow disk. The disk shown in FIG. 3 is provided with a curved aperture 4b on the surface thereof. In case of using such aperture, the region through which the illuminating light passes is formed in a line shape, and accordingly, the region illuminated on the specimen by the objective lens is also formed into a line shape. As the driving rotation of the motor 5 performed, the line illuminating the specimen is moved, and the line formed on the two dimensional photoelectric detector 11 is also moved to make it possible to obtain the two dimensional shape of the specimen.
According to a confocal scanning microscope using a rotation disk, it has an advantage that it is possible to obtain higher image acquisition speed in comparison with a beam deflection confocal scanning microscope, which obtains the image in serial manner using a beam deflector. The limitation of the measuring speed is decided by the image acquisition speed of the two dimensional photoelectric detector, and it is general to acquire images at a rate of thirty frames per second. However, according to the recent improvement of the image acquisition speed of the two dimensional photoelectric detector, the confocal scanning microscope capable of obtaining a thousand frames per second has been realized.
However, it has a defect that the resolution in the direction of the optical axis is decreased because a plurality of points instead of one point or a wide region on the specimen should be illuminated in order to process the parallel signals.
FIG. 4 shows such effect by drawing it. When the specimen 8 is positioned on the focal plane of the objective lens 7, the light reflected from the specimen is accurately collected on the aperture by the tube lens 6 to thereby make a great amount of the lights pass through the aperture as shown in (a) of FIG. 4. In this case, the collected reflected light does not affect the neighboring apertures.
However, when the specimen is gotten away of the focal plane of the objective lens 7, the light collected by the tube lens 6 cannot be accurately collected on the aperture from which the illuminating light has been emitted, and it is collected on a position moved toward the direction of the optical axis. In such case, the reflected light passes through the aperture from which the illuminating light is emitted as well as the neighboring apertures to reduce the enhancing effect of the resolution in the direction of the optical axis according to the confocal principle.
FIG. 5 shows the change of the resolution in the direction of the optical axis according to the increase of the size of the aperture with respect to the confocal scanning microscope using a single aperture and the confocal scanning microscope using multiple apertures. It is necessary to increase the size of the aperture to obtain a measurable great amount of light. However, as shown in FIG. 5, in case of the confocal scanning microscope using the multiple apertures, it is shown that a value of the resolution in the direction of the optical axis can be increased to reduce the capability of the microscope according to the increase of the size of the aperture.
Thus, in case of the confocal scanning microscope using the conventional rotation disk, the entering light reflected at the specimen from the light illuminated at the neighboring apertures acts as a kind of noise to reduce the capability of the microscope in the direction of the optical axis.
Another problem of the conventional technology is a vibration and sampling. It is necessary to prepare the rotating motor to rotate the Nipkow disk, however, it can cause the problem of vibration in the whole optic system. Also, in case of using the two-dimensional photoelectric detector having a high image acquisition speed, a distortion of the image can be produced because the rotation speed of the Nipkow disk is not sufficient.
FIG. 6 is a schematic view of a conventional confocal scanning microscope. As shown in the drawing, the conventional confocal scanning microscope 10 comprises a light source 12, a beam space filtering/expanding device 14, a beam splitter 16, a scanning device 18, an objective lens 20, a collecting lens 22, an aperture shaped as a pinhole, and a photoelectric detector 26.
In the conventional confocal scanning microscope, the light emitted from the light source 12 passes through the beam space filtering/expanding device 14 to become parallel lights, and the parallel lights are reflected at the beam splitter 16 to enter into the scanning device 18. Then the parallel lights, the propagating direction of which is changed by the scanning device, are collected on the specimen 8 by the objective lens 20. The fluorescent light or light reflected from the specimen passes through the objective lens 20, the scanning device 18, and the beam splitter 16, and then is collected on the pinhole shaped aperture 24 by the light collecting lens 22. In this instance, the lights reflected or made to be fluorescent at the focal plane of the objective lens 20 among the lights reflected or made to be fluorescent at the specimen 8 form a focus on the pinhole shaped aperture 24 and are measured by the photoelectric detector 26 after they pass through the aperture. The lights reflected or made to be fluorescent at a region without the focal plane form a focus before or after the pinhole shaped aperture so that a great portion of the lights cannot pass through the pinhole shaped apertures to thereby decrease the intensity of the lights measured at the photoelectric detector. It is possible to observe the inside organ of the object because information emitted from the focal plane of the objective lens 20 can be obtained by using such principle. Also, the resolution in the horizontal direction can be improved, because lights emitted from a point remote from the focus can be filtered by the pinhole shaped aperture although they are on the focal plane.
However, there is a problem that the confocal scanning microscope 10 using the pinhole shaped aperture 24 requires a lot of time to obtain one two dimensional image due to the limitation of the scanning speed of the scanning device 18. High measuring speed can be sometimes obtained to settle such problem by using an accousto-optic deflector in the scanning device, however, in such a case, it causes a defect that a great calculation load is applied to the processing of the signal and a computer is required requisitely.
FIG. 7 is a schematic view of a confocal microscope spectrally encoded at one direction of the two dimensional plane of the specimen by using a diffraction grating. As shown in the drawing, the conventional microscope comprises a optic fiber 71, a lens 72, a diffraction grating 73, and a specimen 74.
In such a structure, the lens 72 collects the light emitted from the dismal end of the optic fiber 71. In this instance, the light emitted from the optic fiber 71 becomes to use a broad band light source having various wavelengths. Because the diffraction grating 73 differs in the propagating angle of a first-order beam according to the wavelength of the light, each light having a wavelength 1, a wavelength 2, and a wavelength 3 are met at points on the specimen different from each other, as shown in the drawing. In this instance, lights reflected at the specimen passes through the diffraction grating 72 and the lens 73 again to thereby be collected at the dismal end of the optic fiber 71, and the collected lights are transferred to the other end of the optic fiber. Thus, because lights of different wavelengths and the coordinates on the specimen can be matched in one direction on the specimen plane, it is advantageous that scanning is not required in the matched direction.
However, it is necessary to deflect the lights in the direction which is not matched by transporting the dismal end of the optic fiber in the direction vertical to the matched direction (a direction vertical to the ground in FIG. 7), or by mounting a beam deflector between the optic fiber 71 and the diffraction grating 73 so as to acquire all the two dimensional images of the specimen.
Thus, when a transporting portion is to be mounted, vibration of the system can be produced according to the movement of the transporting portion to decrease the reliability of the measurement. Further, a piece of information is obtained in the matched direction, and the beam is moved in a direction vertical to the matched direction with receiving signals in series and performing them so that a lot of time is required to process the signals to thereby decrease the image acquisition speed. Also, the used beam deflector or the transporting device for the optic fiber is high cost to become a primary factor of increasing the production cost.